Halogen-containing heterocyclic compound and liquid crystal composition

Abstract

A novel liquid crystalline, halogen-containing heterocyclic compound having a characteristic that even when its S c * phase is supercooled, no other smectic phases appear, and a liquid crystal composition containing the same are provided, which compound is expressed by the formula ##STR1## wherein R 1 and R 2 each represent an alkyl group of 2 to 18 carbon atoms; X represents --N═ or --CH═; Y represents F or Cl; n represents an integer of 0 to 10; and a symbol * represents an asymmetric carbon atom.

What we claim is: 
     
       1. A liquid crystalline, halogen-containing heterocyclic compound expressed by the formula ##STR23## wherein R 1  represents C 2  H 5  and R 2  represents an alkyl group of 6 to 12 carbon atoms; n represents an integer of 3 to 7; and the symbol * represents an asymmetric carbon atom. 
     
     
       2. A compound according to claim 1 wherein said compound is an optically active substance based on the asymmetric carbon atom in said formula (I). 
     
     
       3. A compound according to claim 1 wherein said compound is a racemate. 
     
     
       4. A chiral smectic C liquid crystal composition comprising at least two components at least one of which is a liquid crystalline, halogen-containing compound as set forth in claim 1. 
     
     
       5. A liquid crystal composition according to claim 4 wherein said compound is an optically active substance. 
     
     
       6. A liquid crystal composition according to claim 5, further containing a racemic, halogen-containing heterocyclic compound. 
     
     
       7. In a light switching element employing a chiral smectic C liquid crystal composition, the improvement wherein a composition according to claim 4 is employed. 
     
     
       8. A compound according to claim 1 wherein R 1  represents C 2  H 5 , R 2  is C 8  H 17  and n is 5.